1. Field of the Invention
The present invention relates to a semiconductor light emitting element array including a plurality of semiconductor light emitting elements such as LEDs, and also to an illuminator using such an array.
2. Description of the Related Art
FIG. 4 shows a conventional semiconductor light emitting element array disclosed by JP-A-2005-79202. In the illustrated semiconductor light emitting element array X, a plurality of semiconductor light emitting elements Ed are provided on a substrate 91. Each of the semiconductor light emitting elements Ed has a multilayer structure consisting of an n-GaN layer 92, an active layer 93 and a p-GaN layer 94. Electrons injected from the n-GaN layer 92 and holes injected from the p-GaN layer 94 recombine in the active layer 93, whereby blue light is emitted. The blue light emitted from the active layer 93 travels through a p-side electrode 95, which is transparent, and then enters a fluorescent layer 96. The fluorescent layer 96 contains fluorescent particles, which convert part of the blue light into yellow light. The yellow light obtained by the conversion mixes with the remaining blue light to change into whitish light, which is emitted from the upper surface of the fluorescent layer 96.
The conventional array, however, suffers the following problem when its brightness is to be increased.
The fluorescent layer 96 is made of a resin material mixed with fluorescent particles. The refractive index of the resin material greatly differs from that of GaN (which is suitable for emitting blue light). Accordingly, when the blue light travels from the p-GaN layer 94 to the fluorescent layer 96, a large part of the blue light is subjected to total internal reflection. As a result, the emission efficiency, i.e., the ratio of the amount of light emitted from the fluorescent layer 96 to the amount of light produced at the active layer 93 is not satisfactorily high.
Further, when a current is applied to energize the semiconductor light emitting elements Ed, the n-GaN layer 92, the active layer 93 and the p-GaN layer 94 are heated. Since most part of the semiconductor light emitting elements Ed is covered by the fluorescent layer 96 mainly composed of resin, heat is unlikely to escape. Heat is also generated by the color conversion of the blue light at the fluorescent layer 96. This heat is trapped in the fluorescent layer 96. As the amount of current to be applied to the semiconductor light emitting element array X increases, more heat is produced. In light of these, it has been desired to enhance the heat dissipation of the array X, so that the array X can be more bright.